Enzyme-catalyzed reactions have the advantages of proceeding with great chemical specificity under relatively mild conditions, and often accomplish what man finds difficult, if not impossible, to duplicate in the laboratory. For such reasons there is increasing emphasis on the use of enzymatic processes on a commercial scale. One example, of many which could be cited, is the conversion of glucose to fructose using glucose isomerase.
Enzymes are water soluble, and if they are merely used in aqueous solutions recovery of enzymes for reuse is difficult and expensive. Using the enzyme only once affords a process which is relatively expensive. Consequently, many techniques have been developed for immobilizing the enzyme in such a way that substantial enzymatic activity is displayed while the enzyme itself remains rigidly attached to some water-insoluble support, thereby permitting reuse of the enzyme over substantial periods of time and for substantial amounts of feedstock. One illustration of a method for immobilizing an enzyme is found in U.S. Pat. No. 4,141,857, where a polyamine is absorbed on a metal oxide such as alumina, treated with an excess of a bifunctional reagent, such as glutaraldehyde, so as to cross-link the amine, and then contacting the mass with enzyme to form covalent bonds between the pendant aldehyde groups and an amino group on the enzyme. The support matrix prepared according to the aforementioned invention has great utility in immobilizing reactive chemical entities, enzymes being but one class of such reactive chemical entities.
Generally, immobilized enzyme systems are prepared by contacting a suitable solution containing the enzyme with the support matrix, removing the excess of enzyme solution, and recovering the resulting immobilized enzyme system. Because of the relatively high cost of enzymes, it is highly desirable to maximize enzyme utilization. Among the identifiable characteristics measuring enzyme utilization in an immobilized enzyme system are included the activity and half life of the immobilized enzyme system, and the coupling efficiency of the enzyme to the support matrix. A discovery leading to this invention is that pretreatment of a support matrix with a source of divalent magnesium ions enhances the utilization and immobilization of glucose isomerase.